How to count number of particular child occurrence in firebase for Android in Java

Question

I am making an attendance app and I need to count the particular student attendance from the Firebase. I need to count the number of "prof" occurrence and I am new to this.

 DatabaseReference attendance = FirebaseDatabase.getInstance().getReference("Attendance");
    attendance.addValueEventListener(new ValueEventListener() {
        @Override
        public void onDataChange(@NonNull DataSnapshot dataSnapshot) {
            for (DataSnapshot snapshot : dataSnapshot.getChildren()) {
                totaldays++; // total class days
                if(snapshot.child("name").getValue(String.class).equals("prof")){
                    //count no of days present
                }
                Log.e(snapshot.getKey(), snapshot.getChildrenCount() + "");
            }
            Log.e(TAG, totaldays + "");
        }
        @Override
        public void onCancelled(@NonNull DatabaseError databaseError) {}
    });

But the result is showing null value.

You have two levels that seem to be dynamically generated (the date, and the dcbch.../hello) under the node that you're querying (`Attendance`). Firebase can only return results that are at a fixed path under each child of the node where you run the query. See https://stackoverflow.com/questions/27207059/firebase-query-double-nested — Frank van Puffelen, Jul 05 '18 at 03:50

Alex Mamo · Answer 1 · 2018-07-05T10:03:36.423

In order to solve this, you need to change your database structure. You cannot query your database since your nodes are dynamically generated. As @FrankvanPuffelen mentioned in his comment, the nodes that are causing you troubles are: 04Jul2018 with dcbch... and 05Jul2018 with hello. Because Firebase can only return results that are at a fixed path under each child of the node, to solve this, I recommend you create the date as a property. This is how it can be done and this is how your database structure should look like:

Firebase-root
   |
   --- dcbch..._dkjh...
        |
        --- Prof
             |
             --- email: "profeamil@gmail.com"
             |
             --- name: "prof"
             |
             --- present: true
             |
             --- date: 1530784439 //Current timestamp

And here is the corresponding query:

DatabaseReference rootRef = FirebaseDatabase.getInstance().getReference();
Query query = rootRef.orderByChild("Prof/name").equalsTo("prof");

Now you can attach a listener and use getChildrenCount() method on the DataSnapshot object to get the number of occurrence.

yes I tried as you said and it work. thanks, but I don't want to change the database structure. — SAP MCMXCIV, Jul 09 '18 at 05:05
Unfortunately, there is no way to achieve this using your database structure. — Alex Mamo, Jul 09 '18 at 09:30

score 0 · Answer 2 · answered Jul 05 '18 at 07:25

0

If there is a prof occurrence you can add that child data in a list. In this way you can get the number of childs by using list.size() and also use this list of data in other operations if you have.

answered Jul 05 '18 at 07:25

parag pawar

193
3
13

score 0 · Answer 3 · answered May 10 '20 at 04:58

its very simple to count any field child in the root reference

for example you have a root name attendance then you count to name where type is professor

databaseReference = FirebaseDatabase.getInstance().getReference().child("Attendance").child(istrustnumberavailable);
    databaseReference.limitToFirst(5);

    Query query = databaseReference.orderByChild("name").equalTo("prof");

    ChildEventListener removedListener = query.addChildEventListener(new ChildEventListener() {
        @Override
        public void onChildAdded(@NonNull DataSnapshot dataSnapshot, @Nullable String s) {

            if (dataSnapshot.exists()){

              long  count=  dataSnapshot.getChildrenCount();


            }


        }

        @Override
        public void onChildChanged(@NonNull DataSnapshot dataSnapshot, @Nullable String s) {

            if (dataSnapshot.exists()){

                long  count=  dataSnapshot.getChildrenCount();


            }


        }

        @Override
        public void onChildRemoved(@NonNull DataSnapshot dataSnapshot) {

            if (dataSnapshot.exists()){

                long  count=  dataSnapshot.getChildrenCount();


            }



        }

        @Override
        public void onChildMoved(@NonNull DataSnapshot dataSnapshot, @Nullable String s) {


        }

        @Override
        public void onCancelled(@NonNull DatabaseError databaseError) {

        }
    });

How to count number of particular child occurrence in firebase for Android in Java

3 Answers3